In the present study we seek to: (1) assess the frequency distribution, median values, lability, responsivity, and presence of daily rhythms, of arterial pressure, heart rate, cardiac output, total peripheral resistance, renal blood flow, baroreceptor sensitivity, and levels of circulating catecholamines, angiotensin, and dopamine-beta-hydroxylase in individual chronically instrumented freely moving cats; (2) examine the effects of interruption of baroreceptor reflexes centrally by brainstem lesions which destroy the nucleus tractus solitarii (NTS) thereby producing labile hypertension, on these parameters; (3) attempt to produce sustained arterial hypertension in centrally debuffered animals by behavoiral (classical and instrumental) conditioning of arterial pressure; (4) to define the cardiodynamic basis of such hypertension; (5) to identify any characteristic cardiovascular events or reactivity in normal animals which will predict the susceptability of that animal to the development of labile and ultimately sustained arterial hypertension.